<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
<style>
P{
    color:red;}</style>
<!--  -->
<style>
    .one{
  font-family:宋体;
  fongt-size:24px;
  color:red;  
    }
    .two{
    font-family:宋体;
    fongt-size:18px;
    color:green;
    }
    .three{
     font-family:宋体;
     fongt-size:15px;
     color:blue;
     }
</style>
</head>
<style>
#one{
font-size:18px;}
#two{
font-size:24px;}</style>
<body>
<p style="color:red;">段落标志</p>
<h1 class="one">选择器</h1>
<h1 class="two">选择器</h1>
<h1 class="three">选择器</h1>
<p id="one">ID选择器</p>
<p id="two">ID选择器</p>

</body>
</html>